1. Field of the Art
The present invention relates generally to a dual-type damper device, and more particularly to such a damper device for absorbing vibration of, for example, a rotation axle of an internal combustion engine, so as to reduce vibration and noise caused by the vibration of the rotation axle or the engine.
2. Related Art Statement
Generally, a rotation axle of an internal combustion engine, such as a crankshaft, is subjected to a variable torque, while being rotated, and the rotation axle or the engine produces very complex vibration and/or noise. The rotation axle may be broken due to the complex vibration.
In the above-indicated background of the art, a method has been employed of attaching a flywheel to a rotation axle of an engine of an automotive vehicle, in order to level the variable torque exerted to the rotation axle. Further, the Japanese Utility Model Applications laid open under Publication Nos. 55-135838 and 56-115050 disclose a so-called dynamic damper device, a torsional damper device which incorporates a secondary vibration system. The torsional damper device has a generally cylindrical shape and is joined to a rotation axle (primary vibration system) of an engine. The secondary vibration system is adapted to resonate with the rotation axle, so as to absorb or restrain vibration and/or noise caused by the vibration of the rotation axle.
There is known an example of such a torsional damper device which comprises a damper pulley including a boss portion joined to a rotation axle, such as a crankshaft, a damper-mass member disposed radially outwardly of the damper pulley such that the damper-mass member and the damper pulley are concentric with each other, and a buffer member in the form of a cylindrical resilient member interposed between the damper pulley and the damper-mass member. The resilient member is made of a rubber material or the like. The torsional damper device is designed to reduce vibration and/or noise produced by the engine, by means of narrowing resonance amplitude of the torsional vibration of the rotation axle (crankshaft).
However, vibration produced by the rotation axle is a complex vibration including two main components, torsional vibration and bending vibration (vibration in directions perpendicular to an axis of the rotation axle), and takes a variety of vibration modes depending upon how the rotation axle or the engine is supported by other members. Conventional dynamic damping devices, such as the torsional damper device as indicated above, have been unsatisfactory to damp such complex vibration.
This is because the torsional damper device is capable of damping the torsional vibration of the rotation axle, but incapable of damping the bending vibration of the same. The torsional damper device effectively restrains the torsional vibration through relative displacement between the damper pulley and the damper-mass member (secondary vibration system) due to shear deformation of the cylindrical resilient member therebetween. In order to obtain the desired damping effect on the torsional vibration of the rotation axle, the cylindrical resilient member of the torsional damper device has a comparatively low spring constant in the directions perpendicular to the axis of the rotation axle. And, the thickness of the resilient member is limited to a small value. The cylindrical resilient member having a low spring constant cannot effectively damp the bending vibration. This is because the resilient member having a low spring constant cannot produce a large tensile or compression deformation to damp the bending vibration. In short, the conventional torsional damper device is effective against the torsional vibration of the rotation axle but ineffective against the bending vibration.
In recent years there has been also proposed a dual-type damper device which incorporates a pair of damper-mass members. The dual-type damper device is joined to a crankshaft of an internal combustion engine, for the purpose of dealing with complicated vibration associated with increased operating performance of the engine.
This dual-type damper device has a construction in that a conventional torsional damper device which has a first damper-mass member for damping the torsional vibration further incorporates a second damper-mass member of cylindrical shape, in an inner space of a cylindrical portion of a damper pulley, concentrically with the cylindrical portion, and in between an inside surface of the damper pulley and an outside surface of the second damper-mass member is interposed a cylindrical resilient member with a thin wall. In other words, in comparison with the conventional torsional damper device, the proposed dual-type damper device has newly employed a member serving as another first damper-mass member for damping the torsional vibration. This dual-type damper device is unsatisfactory to damp the vibration of the rotation axle which includes the bending vibration.
Any one of the above-identified conventional damper devices which are used for absorbing or restraining vibration caused by the rotation axle, are effective against only the torsional vibration and not effective against the bending vibration. That is, the conventional damper devices are not effective against the vibration including both the tosional and bending vibrations. Therefore, those devices do not reduce vibration and/or noise caused by a crankshaft of an internal combustion engine. A noise around 350 Hz caused by the bending vibration of the crankshaft makes an uncomfortable knocking noise. The conventional damper devices are incapable of damping the noise around 350 Hz caused by the crankshaft of the internal combustion engine.